Microorganisms such as bacteria and viruses cause serious infectious diseases such as tuberculosis, cholera, hepatitis and meningitis. To diagnose and cure bacterial infections requires rapid and early identification of specific disease causing pathogens in clinical specimens. Several bacterial infections do not show characteristic symptoms initially, which requires sensitive and specific tools to diagnose infections.
Helicobacter pylori infection is one of the most common bacterial infections in humans. The prevalence of H. pylori infection is worldwide and may be as high as 80% in developing countries and up to 40% in developed countries. However, the mode of transmission, the natural history, and other aspects of the epidemiology of H. pylori infection are still unclear. Presence of Helicobacter pylori bacteria in gastric mucosa and epithelia may be associated with chronic gastritis, peptic and duodenal ulcers, and gastric cancers.
Detection of H. pylori is generally accomplished in two ways: (1) directly, by examining a stomach biopsy by histology, cell culture, and other methods to analyze tissue specimens; or (2) indirectly, by testing a sample of peripheral blood serum for circulating antibodies against H. pylori. Some methods require endoscopy with a biopsy. Direct detection methods currently available for H. pylori, include bacterial culture, histology, serology, stool antigen test, rapid urease test (Campylobacter-like organism or CLOtest), isotope urease breath test, and conventional polymerase chain reaction (PCR).
The PCR based methods are sensitive and specific when compared to the urease assay in the presence of other urease-positive bacteria. PCR based methods are relatively inexpensive and produce results faster than bacterial culture, because culturing H. pylori is lengthy and is not possible in many situations. Conventional PCR generally uses a set of primers to amplify a genetic region in H. pylori. PCR tests for various bacteria, including H. pylori, are available for a broad spectrum of specimens, including laboratory cultures and clinical samples. Although conventional PCR based detection methods have many advantages, there are some disadvantages due to both frequent false-positive and false-negative results. The presence of polymorphisms at the primers' binding sites may lead to low specificity in conventional PCR tests.